Bidirectional Forwarding Detection (BFD) is an IETF (Internet Engineering Task Force) standard that allows two endpoints to monitor reachability over a link or a network by both ends periodically sending “hello” packets to each other. It is an efficient and generic hello/keepalive protocol that is widely used by many applications, including, for example, IGPs (Interior Gateway Protocols), EGPs (Exterior Gateway Protocols) and protocols such as HSRP (Hot Standby Router Protocol), ICCP (Inter-Chassis Communication Protocol), and others.
The IETF BFD working group has been defining a more efficient unidirectional monitoring mechanism called Seamless Bidirectional Forwarding Detection (S-BFD).
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.